geant4 trackingAction

geant4 trackingAction

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在 tractAction 类中实现的 PreUserTrackingAction(const G4Track* theTrack) 和 PostUserTrackingAction(const G4Track* theTrack) 的区别 ?

通过输出，判断两者的区别

PreUserTrackingAction track ID = 1
PreUserTrackingAction parent ID = 0
PreUserTrackingAction Current Step ID = 0
PreUserTrackingAction Particle = Am241
PreUserTrackingAction Position = (0,0,0)
PreUserTrackingAction KineticEnergy = 0
PreUserTrackingAction Momentum = (0,0,-0)
PreUserTrackingAction GlobalTime = 0
PreUserTrackingAction LocalTime = 0
PreUserTrackingAction ProperTime = 0

PostUserTrackingAction track ID = 1
PostUserTrackingAction parent ID = 0
PostUserTrackingAction Current Step ID = 1
PostUserTrackingAction Particle = Am241
PostUserTrackingAction Position = (0,0,0)
PostUserTrackingAction KineticEnergy = 0
PostUserTrackingAction Momentum = (0,0,-0)
PostUserTrackingAction GlobalTime = 4.03267e+18
PostUserTrackingAction LocalTime = 4.03267e+18
PostUserTrackingAction ProperTime = 4.03267e+18


PreUserTrackingAction track ID = 3
PreUserTrackingAction parent ID = 1
PreUserTrackingAction Current Step ID = 0
PreUserTrackingAction Particle = alpha
PreUserTrackingAction Position = (0,0,0)
PreUserTrackingAction KineticEnergy = 5.4429
PreUserTrackingAction Momentum = (16.6282,-161.089,-119.912)
PreUserTrackingAction GlobalTime = 4.03267e+18
PreUserTrackingAction LocalTime = 0
PreUserTrackingAction ProperTime = 0

PostUserTrackingAction track ID = 3
PostUserTrackingAction parent ID = 1
PostUserTrackingAction Current Step ID = 154
PostUserTrackingAction Particle = alpha
PostUserTrackingAction Position = (1.48547,-13.0785,-9.85898)
PostUserTrackingAction KineticEnergy = 0
PostUserTrackingAction Momentum = (0,-0,-0)
PostUserTrackingAction GlobalTime = 4.03267e+18
PostUserTrackingAction LocalTime = 1.10012
PostUserTrackingAction ProperTime = 1.09875

• PreUserTrackingAction() 和 PostUserTrackingAction() 指的是同一个 track.
• PreUserTrackingAction() 返回的是该 track 第一个 step 提取出的信息。
• PostUserTrackingAction() 返回的是该 track 最后一个step 提取出的信息。

从 trackAction 中可以提取哪些信息？

• trackID
• parent ID
• current step ID
• particle name
• current step position
• current step kinetic energy
• current step momentum
• golbal time: 从 event 起点到当前 step 的时间，单位是 ns
• local time: 从 tarck 起点到当前 step 的时间
• proper time: time in its rest frame since the track was created

解释 GlobalTime

使用 241Am 放射源，其半衰期为 432.6 y，模拟 10w 次事件，提取 trackID = 1 时，postuserTrackingAction 中的 GlobalTime. 理论上，将提取得到的 GlobalTime 做直方图，是指数衰减的曲线。实际的模拟结果如下，这里横坐标是 GlobalTime/432.6y 的结果，理论上该曲线为 $y = 100000e^{-0.693t}$，实际的拟合结果很接近。

代码如下：Am241Life.cc

const double half_life = 432.6*365*24*3600*1000000000;

void Am241Life()
{
  ifstream file;
  file.open("hanX3Copy", ifstream::in);
  if (!file) {
    cout << "cannot open the file." << endl;
    return ;
  }

  cout << "half time = " << half_life << endl;
  vector<double> life_unit;
  double life_ns;
  
  while (1) {
    file >> life_ns;
    if (!file.good()) break;
    life_unit.push_back((double)life_ns/half_life);
  }

  file.close();

  cout << life_unit.size() << endl;
  for (int i=0; i<10; i++) {
    cout << life_unit[i] << endl;
  }

  TH1D* h1 = new TH1D("h1","h1",10,0.,10.);
  vector<double>::iterator it;
  for (it = life_unit.begin() ; it != life_unit.end(); ++it) {
    h1->Fill(*it);
  }

  h1->Draw();
}

这说明，在使用时间作为 kill track 的限制时，要排除掉第一个 trackID 的 GlobalTime.